Henry Ernest Dudeney/Modern Puzzles/220 - The Fly's Tour

Modern Puzzles by Henry Ernest Dudeney: $220$

The Fly's Tour

I had a ribbon of paper, divided into squares on each side.

I joined the ends together to make a ring, and tossed it down onto the table.

Then I watched a fly land on the ring and walk in a line over every one of those squares on both sides,

returning to the point where it started, without ever passing over the edge of the paper.

Its course passed through the centre of the squares all the time.

How was this possible?

Sources

• 1926: Henry Ernest Dudeney: Modern Puzzles ... (previous) ... (next): Unclassified Problems: $220$. -- The Fly's Tour
• 1968: Henry Ernest Dudeney: 536 Puzzles & Curious Problems ... (previous) ... (next): Unclassified Puzzles: $517$. The Fly's Tour